Generally, a motor-driving device refers to a device that can control a speed of a motor with a high efficiency by varying a voltage and frequency of a power supplied from an external power supply and supplying the power with the varied voltage and frequency to the motor.
FIG. 1 is a perspective view of a conventional motor-driving device. FIG. 2 shows a top view of a conventional power board.
Referring to FIG. 1 and FIG. 2, a conventional motor-driving device may include a base 10, heat-dissipating means 20 disposed below the base 10, and a board assembly 30 disposed above the base 10.
The board assembly 30 includes a power board 31 positioned on the base 10, a cap board 32 (a filter board) disposed on the power board 31, and a control board 33 disposed on side faces of the cap board 32 and power board 31. Though not shown, the board assembly may further include an input/output (IO) board on the cap board 32.
The conventional power board 31 receives power from the IO board (not shown).
Specifically, to supply power to a driver such as a motor, the power board 31 receives AC power from the outside through the IO board, and then converts the AC power into DC power and then rectifies the DC power and then converts the rectified DC power to AC power.
In this connection, referring to FIG. 2, the power from the external power supply may have two types of flows as follows in the motor-driving device.
First, in a main power flow, the AC power input to an input terminal block 1 of the power board 31 is converted trough a rectifying section 2 to DC power including ripple. Thereafter, the DC power smoothed by a DC link of the cap board 32 is again applied to an inverter 3 through a DC terminal 7 of the power board 31. Then, the inverter 3 converts the DC power to AC power and outputs the AC power to an output terminal block 4.
Second, in a signal flow, DC power generated from the DC link 7 may be used as a power source for controlling the motor-driving device. The DC power generated from the DC link 7 may be applied to the control board 33, a gate drive, a sensing and protection circuit 5, and the like.
In this conventional motor-driving device, the power flow and the signal flow may have a noise-vulnerable structure in which an intersection occurs between an output of the rectifying section 2 and an output of the inverter 3, and thus interference therebetween occurs.
Further, the cap board 32 is connected to a grounding screw 6 of the power board through a grounding wire 34 formed on the cap board. The grounding wire 34 connected to the power board 31 extends and is connected to the heat-dissipating means 20.
Such a structure of the conventional motor-driving device may cause malfunction of the device because the grounding wire 34 may absorb a high-frequency noise signal. When the grounding wire 34 touches the heat-dissipating means 20 or the SMPS, a sheath thereof may melt. This may cause power flow or signal flow interruption. Thus, malfunction of the device and burnout of the device may occur.